IMOS - SOOP Underway pCO2 System Overview

Research Project

Researchers: Tilbrook, Bronte (Principal investigator) ,  Tilbrook, Bronte (Principal investigator) ,  AODN Data Manager (Point of contact, Distributes) ,  Akl, John (Processor of) ,  Akl, John (Processor of)
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Brief description The CSIRO Ship of Opportunity Underway pCO2 system is mounted on the Research Vessel Southern Surveyor (IMOS platform code: VLHJ) of the Australian Marine National Facility. CO2 System Overview: The fugacity of carbon dioxide (fCO2) in surface seawater is measured using a General Oceanics Inc. automated system (Model 8050; Pierrot et al 2009). Seawater is sprayed into an equilibration chamber and CO2 in the headspace gas equilibrates with the seawater. The headspace gas is pumped through a thermoelectric condenser followed by a nafion drying tube before flowing through a Licor 7000 non-dispersive infrared gas analyser that is used to measure the CO2 mole fraction (XCO2) of the dried air. The gas flow is stopped temporarily for the CO2 measurements, which are made at atmospheric pressure. A set of four CO2 in-air standards that cover the range of CO2 values expected in the ocean are analysed about every four hours to calibrate the gas analyser. The standard gas concentrations are on the WMO-X2007 mole fraction scale for CO2-in-air. Atmospheric XCO2 (dry) is measured immediately after the standards by pumping clean outside air from an intake on the forward mast of the ship. Seawater intake and ancillary data: The ships seawater intake is located at about 5.5m depth in the bow of the ship. Sea surface salinity is measured using a thermosalinograph (Seabird Electronics SBE21) located next to the CO2 system. A remote temperature sensor (Seabird Electronics SBE 38) located at the intake is used to measure sea surface temperature (SST). The travel time between the intake and CO2 system is typically about 4 minutes with warming usually less than 0.6ºC. The thermosalinograph water is from the same intake, but the supply lines separate after the intake. A comparison of thermosalinograph and equilibrator temperature records shows the temperature difference in the two lines is generally less than 0.1ºC. The thermosalinograph water line travels outside the ship and is typically warmer than the equilibrator. The travel time in water line to the thermosalinograph is 2.5 minutes faster than the equilibrator. Meteorological data, salinity, SST, and ships position and time are taken from the ships logging system. These parameters and the data quality are maintained by the Australian Marine National Facility.

Notes Credit
Australia’s Integrated Marine Observing System (IMOS) is enabled by the National Collaborative Research Infrastructure Strategy (NCRIS). It is operated by a consortium of institutions as an unincorporated joint venture, with the University of Tasmania as Lead Agent.

Notes Credit
Australian Marine National Facility (MNF)

Notes Credit
CSIRO Oceans & Atmosphere